1. Field of the Invention
The present invention relates to a hydraulic brake booster for boosting a hydraulic pressure so as to actuate brakes of a vehicle such as an automobile or a motorcycle.
2. Description of the Related Art
Such a hydraulic brake booster is already known and is disclosed, for instance, in Japanese Examined Patent Publication No. HEI 4-864.
In a conventional hydraulic brake booster, a hydraulic booster adapted to be actuated by a valve piston connected to a brake pedal and a master cylinder adapted to be actuated by a piston of the hydraulic booster are connected to each other in series, and therefore the overall length of the booster so constructed tends to be extremely large, and therefore it is sometimes found difficult to install such a booster in a limited space of a vehicle.
The present invention was made in view of these circumstances, and an object thereof is to provide a hydraulic brake booster that allows constituent elements to be disposed freely, which can easily be installed even in a limited space and which is simple in construction.
To attain the above object, according to a first aspect of the invention, there is provided a hydraulic brake booster comprising:
a primary master cylinder which generates an output hydraulic pressure in response to a brake operation input;
a hydraulic power source;
a fluid tank which stores fluid for the hydraulic power source; and
a proportional booster valve which proportionally boosts an output hydraulic pressure from the primary master cylinder and supplies the output hydraulic pressure so boosted to wheel brakes, the proportional booster valve including:
a casing having a cylinder bore;
a control piston unit defining in conjunction with the cylinder bore, a controlling hydraulic pressure chamber introducing an output hydraulic pressure from the primary master cylinder and a boosting hydraulic pressure chamber generating a boosting hydraulic pressure for actuating wheel brakes, the control piston fitted in said cylinder bore so as to reciprocate between a first position and a second position in response to hydraulic pressures of the controlling hydraulic pressure chamber and the boosting hydraulic pressure chamber, the first position defining the maximum controlling hydraulic pressure chamber, the second position defining the minimum controlling hydraulic pressure chamber;
an inlet valve communicating between the hydraulic power source and the boosting hydraulic pressure chamber in response to the movement of the control piston unit; and
an outlet valve communicating between the boosting hydraulic pressure chamber and the fluid tank in response to the movement of the control piston unit,
wherein the inlet valve is opened and the outlet valve is closed when the control piston unit is located at the first position, and the inlet valve is closed and the outlet valve is opened when the control piston unit is located at the second position,
whereby a hydraulic pressure boosted in proportion to the hydraulic pressure of the controlling hydraulic pressure chamber is generated in the boosting hydraulic pressure chamber.
Further, according to a second aspect, there is provided a hydraulic brake booster comprising:
a primary master cylinder which generates an output hydraulic pressure in response to a brake operation input;
a hydraulic power source;
a fluid tank which stores fluid for the hydraulic power source; and
a proportional booster valve which proportionally boosts an output hydraulic pressure from the primary master cylinder and supplies the output hydraulic pressure so boosted to wheel brakes, the proportional booster valve including:
a valve housing having a cylinder bore, a valve bore communicating with one end of the cylinder bore, a hydraulic power source port communicating with said hydraulic power source and opened to an inner circumferential surface of the valve bore, a return port communicating with the fluid tank and opened to the inner circumferential surface of the valve bore and a booster port communicating with the wheel brakes;
a control piston slidably fitted in the cylinder bore so as to be reciprocate between a first position and a second position and defining at the other end of the cylinder bore a controlling hydraulic pressure chamber for introducing the output hydraulic pressure from the primary master cylinder; and
a spool valve body connected to the control piston and slidably fitted in the valve bore,
wherein when the control piston is located at the first position through boosting the hydraulic pressure in the controlling hydraulic pressure chamber, the spool valve body establishes a communication between the hydraulic power port and the booster port, and
when the control piston is located at the second position through reducing the hydraulic pressure in the controlling hydraulic pressure chamber, the spool valve body establishes a communication between the return port and the booster port.